Drilling tool having an adjustable scraping angle



I United States Patent [1113550 2 [72] Inventors Jean-Claude Raynal; 56] References cited {211 ggg zi France UNITED STATES PATENTS 22 il July 7, 19 9 1,893,693 I/ l 933 Aloi l75/292X [45] Patented Dec. 29, 1970 2,064,273 12/ l 936 Scott l75/342X [73] Assignee Societe Nationale Des Petroles DAquitaine 2,198,349 4/1940 WaXlel 381x Courbevoie, France, 2,243,319 5/1941 Ross 175/319 a corporation ofF -ance 2,648,526 8/1953 Lanchester. l [32] Priority July 10, 1968 2,850,265 9/1958 Cruthers..... 175/289X France Bodine [31] 158,667 Primary Examiner-Marvin A. Champion Assistant Examiner-Richard E. Favreau Attorneyl-lolcombe, Wetherill & Brisebois [54] DRILLING TOOL HAVING AN ADJUSTABLE 5 ABSTRACT: A tool for use in drilling rock, comprising a too] mg g body having regularly spaced cylindrical cavities therein, sup- [52] US. Cl. 175/289, porting arms each having at its upper part a cylindrical portion 175/342 adapted to be positioned in one of said cylindrical cavities in [51] Int. Cl E21b 9/08, the tool body and capable of rotational and sliding movement E2 lb 9/26 therein, the supporting arms being provided with bearings and [50] Field of Search 175/342, carrying cutting wheels, the said wheels being adjustable so as 381, 289, 319, 292,286, 331, 356, 365, 366, 273, to be adapted to be set, at the cutting face of the tool, in de- 279 pendence upon the load applied to the tool.

DRILLING TOOL HAVING AN ADJUSTABLE SCRAPING ANGLE The present invention relates to a drilling tool having an adjustable scraping angle, for use in drilling boreholes in geological formations (referred to hereinafter simply as rock).

Drilling tools for this purpose may comprise several cutting wheels turning freely relatively to journals or bearings which are mounted on an arm forming the body of the tool.

With these tools, the projections of the axes of the cutting wheels on a plane perpendicular to the axis of the tool are generally not coincident.

When the axes of the cutting 'wheels are projected in this way, they form with the projections of the theoretical axes which pass, on the one hand, through the centers of the circles at the junctions of the bearings and the supporting arms and, on the other hand, through the axis of the tool, angles which are called the scraping angles or scraping characteristics. For any given tool, these angles are equal. They determine the working of the tool. If the scraping angle is zero and if the cutting wheels have a suitable angle, the said wheels roll on the surface of the rock which is acted upon and the tool operates strictly by percussion. On the other hand, if the scraping angle is large, the tool operates in addition by stripping off material, due to the tool sliding on the surface of the rock which is being attacked.

Tools which have a strong scraping action are used for soft rocks. On the contrary, for hard rocks, the tools used should have a very small scraping angle. Moreover, tools with a strong scraping action are employed at high speeds of rotation and with small pressures on the tool. On the contrary, for the tools having a small scraping angle, the speeds of rotation used are low and the applied pressures are high. v

The rock formations which are encountered generally comprise alternating strata of rocks of variable hardness, the hardness varying about a certain mean; the estimation of the hardness makes it possible to select the grade of tool which should be employed. It is one object of the invention to provide a tool which is capable of being adapted to these variations. To this end the invention provides a tool, which is such that if the rock encountered becomes harder, the increase in the pressure which is exerted on the tool causes a decrease in the scraping angle of the cutting wheel or wheels of the tool.

The tool provided according to the present invention comprises supporting arms equipped with' journals about which cutting wheels are able to turn freely, the said supporting arms having cylindrical portions at their upper parts, and the tool further comprising a tool body having regularly spaced cylindrical cavities receiving the cylindrical portions of the supporting arms, a first element having at least one orifice, applied to the upper faces of the supporting arms, a second element having at least one orifice and integral with the tool body, springs adapted to bear on the said first element and on the said second element, and a sliding arrangement adapted to position the supporting arms during rotation of the tool, in dependence upon the applied load transmitted by the springs.

In one preferred embodiment of the invention, keys are provided which are fast with the tool body and are capable of sliding in helical grooves machined in the respective supporting arms; these ensure correct positioning during rotation of the supporting arms.

The invention will be more fully understood from the following description, given by way of example only, of one form of tool constructed according to the invention, reference being made to the accompanying drawings in which:

FIG. 1 is an elevational view of the tool, partly in section;

FIG. 2 is an elevational view from a direction at right angles to the view shown in FIG. 1, showing the position of a helical groove which will be referred to hereinafter, and

FIG. 3 is a sectional view on a plane perpendicular to the longitudinal axis of the tool, showing the positions of various axes.

Referring to FIG. I, the reference 1 indicates one of the cutting wheels of the drilling tool. This wheel is formed with cutting teeth or projections (not shown). The cutting wheel 1 is able to rotate freely relatively to a bearing mounted on the supporting arm 2. The upper portion of this supporting arm is of cylindrical form and is adapted to engage in a cavity, which is likewise cylindrical, formed in the tool body 4. The upper face of the supporting arm 2, indicated at 8, is adapted to be applied against a ring 6 having an orifice provided for the passage of the mud or slurry resulting from the drilling operation. A series of springs 5 bear on the ring 6. A disc 7, which is made fast with the tool body 4, for example by being screwed on to the said body, bears against the upper part of the stack of springs 5. There is a recess 9 between the ring 6 and the tool body. The size of this recess is variable as a function of the pressure applied to the tool, due to the variable compression of the springs 5. A screw-thread 10 permits the tool to be connected to a drilling assembly (not shown). A key 3 fast with the tool body is engaged in a helical groove 11 formed in the surface of the supporting arm 2.

FIG. 2 shows an external view of the upper portion of the tool according to the invention. The supporting arm can be seen at 2; the upper portion of the arm 2 is cylindrical and is formed with the helical'groove, the position of which is indicated in dotted lines at 11, while the tool body is shown at 4 and the key fast with the said tool body is shown at 3.

FIG. 3 shows a diagrammatic section of the tool body and of three supporting arms, on a plane at the level of the respective keys associated with the arms. The tool has three cutting wheels carried by the three supporting arms. The tool body is represented at 4 and the sections of the supporting arms are represented at 2. The respective keys fast with the tool body 4 are shown at 3. In addition, the axes passing through the centers of the cylindrical upper portions of the supporting arms and through the longitudinal axis of the tool are shown at 12. Thus the positions 12 represent the setting of the cutting wheels for zero scraping angle. Each line 13 is the projection of the axis of the associated cutting wheel, passing through the pivotal axis of the said wheel. The angle contained between each pair of lines 12 and 13 (that is to say the angle 14) is the scraping angle."

During the operation of the tool, this angle is variable. Actually, when a small pressure is applied to the tool, the springs 5 are substantially fully relaxed and the supporting arm is in the lower position, so that the scraping angle is large. This is predetermined at the time when the helical groove is formed. This groove is formed in such a way that, when the cylindrical portions of the arms 2 are driven into the cylindrical cavities in the tool body 4, the scraping angle decreases. Thus, if the pressure on the tool becomes large, the springs are compressed, the upper portions of the arms 2 are engaged to a greater extent in the tool body and the scraping angle decreases by rotation of the supporting arm about its axis.

The result of this is that when the pressure on the tool increases, the scraping angle is decreased and the tool is caused to operate by percussion.

The advantages of the tool provided by the invention arise from the fact that when drilling hard rock it is more efficient to operate by true percussion, whereas it is more efficient when working on soft rock to operate by tearing or stripping. With the tool of the invention adjustment of the scraping angle can be produced by the simple effect of the pressure applied to the tool, which can be easily regulated from the surface, at the mouth of the borehole.

We claim:

1. A tool for drilling rock, comprising a tool body having regularly spaced cylindrical cavities therein, supporting arms each having a cylindrical upper portion adapted to be positioned in one of said cylindrical cavities in said body and capable of rotational and sliding movement therein, said supporting arms being provided with bearings and carrying cutting wheels which are adapted to turn freely about said bearings, a first element in said body, having at least one orifice bearing against said upper portions of said supporting arms, a second element in said body having at least one orifice, spring elements engaged between and bearing against said first and arms, said keys being mounted on said body and each key being adapted to slide in a helical groove formed in the associated supporting arm, said keys acting to position said supporting arms in rotation. 

